1. Field of the Invention
The present invention relates to a cleaning apparatus and a cleaning method for cleaning an object, such as a semiconductor wafer or an LCD (Liquid Crystal Device) substrate.
2. Description of the Related Art
In a process of manufacturing, for example, a semiconductor device, it is necessary that the surface of a semiconductor wafer (hereinafter abbreviated as a wafer), on which the semiconductor device (e.g., an LSI) is to be formed, be kept strictly clean. For this reason, the surface of a wafer is cleaned, if necessary, before and after each manufacturing process or treatment process. In particular, the photolithography process inevitably requires cleaning of the wafer surface.
Conventionally, the cleaning is performed by a scrub cleaning apparatus as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 57-102024 or 62-259447. In the scrub cleaning apparatus, a cleaning body, such as a rotary brush or sponge, is brought into contact with a surface of an object to be cleaned, so that a foreign substance adhered to the surface can be scrubbed off.
In the scrub cleaning apparatus, a mechanism similar to that for regulating a pressure of a stylus of a record player is employed as a mechanism for bringing the cleaning body to the surface to be cleaned. The mechanism has an arm, one end of which is fixed and the other end of which supports the cleaning body. A balance weight, which is lighter than the total weight of the arm, is mounted on the attachment side (the other end) of the arm, so that a contact pressure can be obtained by the difference between the total weight of the arm and the balance weight.
When the cleaning body is in contact with the surface of the object to be cleaned, the degree of the contact pressure is therefore very important, since if the contact pressure is too high, the surface of the object is damaged, resulting in reduction of the manufacturing yield. Therefore, when the cleaning body is to be brought into contact with the surface of the object to be cleaned, the problem is to what degree the contact pressure is set. In the conventional scrub cleaning apparatus, since the contact pressure cannot be set to a specified value, the cleaning body may damage the object to be cleaned during a scrub cleaning time.
Moreover, as the number of times of cleaning is increased, the elasticity and restorability of the brush or sponge (the cleaning body) is reduced, and the cleaning body is put aside, rimpled or rendered nonuniform in density. As a result, the contact pressure initially set cannot be maintained, and the cleaning cannot be performed sufficiently or uniformly. In this case, the contact pressure should be suitably regulated. However, in the conventional scrub cleaning apparatus, since the contact pressure is regulated by means of the balance weight arranged on the arm, it is necessary to adjust the distance between the balance weight and the fulcrum, every time the contact pressure is to be changed. This adjustment procedure is very difficult.